The invention relates to methods and apparatus for producing bags having a recloseable fastener and in particular bags in which such a fastener extends in substantially the same direction as the top and bottom seals of the bag.
It is well known to make bags by a form, fill and seal (FFS) process. The FFS process is well known and will be described herein with reference to vertical, form, fill and seal (VFFS) machines. In such a machine, a web of flexible packaging material is fed over a forming shoulder to form a tube about a vertically oriented filling pipe. The edges of the web are sealed together in the longitudinal direction of the tube and then successive transverse seals are made at bag length intervals by means of opposed sealing jaws. One jaw of an opposed pair usually carries a knife which cuts through the tubular web at each transverse seal to provide a top seal for a completed bag and a bottom seal for the following bag. Product is fed down the forming tube in synchronicity with the sealing jaws so that each package contains a required amount of product.
It is also known to provide bags produced on FFS machines with a recloseable fastener. Such fasteners typically take the form of two elongate elements one of which comprises a rib extending along the length of the element and the other of which has a channel which receives the rib. The arrangement of the elements is such that the rib can be pushed into the channel and will be releasably retained therein to form a fastening. Such fasteners will be referred to herein as zips or zip fasteners.
One approach to applying zips to bags produced on VFFS machines has been to apply the zip to the web before it reaches the forming shoulder. The web approaches the forming shoulder in planes which may be horizontal but are at least transverse to the axis of the forming tube. The zip is fed from a supply reel across the web from one side thereof with the two elements of the zip engaged, ie with the rib received in the channel. At the location at which the zip is to be applied to the web, a length of the zip substantially equal to the width of the bag is cut and then the cut length is secured to the web by means of a heat sealing jaw. In more detail, one of the two elements of the zip is secured to the upwardly facing side of the web by heat welding. The element may be securely welded to the web or tacked onto the web. The web with attached zip then passes over the forming tube and when the opposed sealing jaws meet to form the transverse bag seals, the elements of the fastening strip are simultaneously welded to their respective sides of the bag just below the top seal of the bag.
The invention provides apparatus for securing a fastening strip to a web of packaging material, said apparatus comprising means defining a support surface for said web, said support surface having an elongate recess for receiving said fastening strip, movable sealing means disposed opposite and below said support surface, a retractable support element disposed between said support surface and said sealing means, means for feeding said fastening strip in a lengthwise direction of said recess and between said support element and said support surface and means for holding said fastening strip, the arrangement being such that said support element can be retracted to a position which permits said sealing means to move said web into engagement with said support surface and said fastening strip with said fastening strip received in said recess, said holding means being actuable to hold said fastening strip when said support element is retracted.
The invention also includes a method of securing a fastening strip to a web of packaging material, said method comprising the steps of feeding said fastening strip across said web such that a length of said strip is positioned at a predetermined position relative to said web, providing a support for said fastening strip during said feeding step, applying a holding force to said fastening strip and withdrawing said support, moving said web into engagement with said fastening strip and securing said web to said fastening strip.